In the group 3, 12 cases of stroke or transient ischemic attack occurred within 30 days, including 8 cases of CYP2C19 gene deletion, 4 cases of CYP2C19 gene carriers, 4 cases of vertebrobasilar artery extracranial stenosis, and 8 cases of vertebrobasilar artery intracranial stenosis. Here, CYP2C19 is linked to transient ischemic attack.